The present invention relates generally to a method and apparatus for slitting a sheet material web, and in particular, to a method and apparatus for slitting a sheet material web being wound on a roll.
It is well known in the field of paper making, and particularly in the field of manufacturing tissue products such as facial tissues, bath tissues and paper towels, to provide an apparatus for longitudinally slitting a continuously running sheet material web into two or more strips. Typically, the sheet material web is slit either as it traverses an xe2x80x9copen drawxe2x80x9d before being wound into rolls, before it is dried or after it is wound onto the roll. In the first instance, the area of open draw, where the dried sheet is momentarily unsupported before being wound, provides an ideal place to slit the web. In particular, the slitting device, often configured as a rotary saw blade, can be applied to the web without concern about cutting or otherwise damaging an underlying fabric, which otherwise carries the sheet material web throughout the forming process. Fabrics of this nature can be expensive and difficult to replace.
However, as described in U.S. Pat. No. 5,591,309, issued Jan. 7, 1997 to Rugowski et al., and assigned to Kimberly-Clark Corporation, the same assignee as the present application, open draws are a frequent source of sheet breaks and associated production delays. As a result, tissue sheets often are designed to have high machine direction strengths in order to remain intact as they are pulled through the open draw. However, high machine direction strengths can adversely affect the quality of the web in terms of its desired softness. Therefore, as explained in U.S. Pat. No. 5,591,309, the elimination of open draws in tissue manufacturing can result in a sheet material being made more efficiently at less cost and wish more desirable properties.
When the open draw is eliminated, the sheet material web is typically slit using a water jet prior to drying the web. However, such xe2x80x9cwet slittingxe2x80x9d can result in a degradation of the throughdrying fabric as it is exposed to hot air passing through the slit in the sheet material during the drying stage of the process. Moreover, the slit edges of the sheet material web may not dry evenly due to the pile up of fibers along the slit. Additionally, when the sheet material web is slit prior to drying, the various strips of sheet material web are difficult to control and can become inadvertently interwoven, or overlapped, as they are further carried towards the winding drum and reel spool. Interwoven strips can be more easily damaged and can make the winding process particularly difficult. Moreover, adjacent rolls having interwoven webs can be particularly difficult to separate. Accordingly, the strips of sheet material web are typically required to be spread apart so as to prevent interweaving.
In contrast to slitting the web prior to drying, it is also known in the art to slit the sheet material web as it is wound onto the roll. Slitting apparatuses of this nature typically apply a pressure or guide roller, or like device, to the outermost surface of the roll so as to thereby control the penetration of the slitting device. However, facial and bath tissues typically have relatively low densities, and hence low resistance to compressive forces. Accordingly, it usually is not desirable, or even possible, to allow such a guide roller to contact the roll as it builds so as to thereby control the position of the slitter, and the penetration thereof
Briefly stated, the invention is directed to an apparatus for slitting a sheet material web as it is wound onto a roll. The apparatus includes a slitting device having a track member and a slitting member moveably mounted on the track member. The slitting device is supported adjacent to a roll of sheet material web. The apparatus includes at least one winding drum which supports the sheet material web and a moveable reel spool which is positioned in a parallel, spaced apart relationship with the winding drum. The sheet material web is deposited on the reel spool which moves away from the winding drum as the diameter of the roll formed thereon increases. A control system connects the track member and reel spool and is adapted to move the slitting member on the track member in relation to the position of the reel spool relative to the at least one winding drum so as to maintain the predetermined depth of penetration of the slitting member within the roll. In this way, the control system controls the depth of penetration of the slitting member within the roll as it increases in size so as to maintain the desired penetration of the slitting member within the roll but without the control system or track contacting an outer surface of the roll.
In one aspect of the invention, the slitting device includes a carriage which is moveably mounted on a laterally extending support member. In operation, the operator can move the carriage laterally along the length of the cross member to alter the position of the slit in the sheet material web, or to provide access to the slitting device.
In a preferred embodiment, the track member is pivotally attached to the support member about a horizontal axis. In operation, the track member can be pivoted about the axis to maintain the penetration of the slitting member within the roll, or to move the slitting device completely out of the path of the roll, reel spool or supporting structure.
In yet another aspect, a method is provided for continuously slitting the sheet material web as it is wound onto a roll. The method includes the steps of carrying the web over a winding drum in a longitudinal direction, depositing the web onto a rotating reel spool to form a roll, making a plunge cut with a slitting member to slit the roll after a predetermined number of initial layers are formed on the roll, moving the reel spool relative to the winding drum as the size of the roll increases and moving the slitting member relative to the position of the reel spool so as to continuously slit the web on the roll while maintaining a predetermined depth of the slitting member within the roll.
The present invention provides significant advantages over other slitting devices. Importantly, the apparatus allows for slitting the sheet material web while it is being wound onto a roll. In this way, the open draw of the forming process can be eliminated so as to reduce waste and improve the quality of the sheet material, but without having to slit the web prior to the drying process, wherein the problems of fabric degradation, fiber build-up at the slit edges and loss of sheet control can be encountered.
Moreover, the apparatus provides for an improved, cleaner cut as compared with webs slit over an open draw because the sheet material web is supported by the underlying layers of web already wound onto the roll. Moreover, since the web is slit as it is wound onto the roll, the problem of interweaving is thereby eliminated, and the rolls can be easily separated.
In addition, the present invention provides an improved method and apparatus for slitting the web on the roll. In particular, the track and control system provide a unique way of maintaining the desired penetration of the blade within the roll without using a guide roller or similar device to contact the outer surface of the roll. This is especially important with the manufacture of tissue rolls wherein the density of the web is relatively low and the roll is less capable of reliably supporting a guide roller. Moreover, bathroom tissue and the like are formed from at relatively fragile sheet material web which can be more easily damaged by contact with a guide roller or similar device.
In addition, since the track and slitting member are not dependent upon or linked to the surface of the roll, and the penetration of the slitting member is not controlled thereby, the penetration of the slitting member can be independently adjusted. In this way, the slitting member can be moved to provide an initial plunge cut in the roll after a predetermined number of initial layers are wound onto the roll, and the depth of the penetration can be easily adjusted to account for varying thicknesses of the sheet material web. The capability to provide a plunge cut through the use of a programmable controller greatly simplifies the mechanism. Moreover, by providing a pivotal attachment, the slitting member can be easily and quickly moved away from the roll if slitting is not desired, in the event of a sheet break or for various other reasons such as avoiding overhead support structure while laterally moving the track above the roll of sheet material.
Additionally, the apparatus can easily be moved laterally to any desired position above the longitudinally moving web, or can be moved completely to the side of the operating line so as to be accessible to the operator for blade changes and the like. Alternatively, a plurality of slitting apparatuses can be positioned above the web so as to enable the operator to make multiple strips of sheet material web. In either situation, the desired slitting operation can be set up quickly, inexpensively and with little or no waste.
Furthermore, the use of a single track overlying the roll eliminates the need for parallel tracks on opposite sides of the roll, and thereby avoids the possibility of binding, within the tracks and reduces the overall cost of making and maintaining the apparatus.